Patterns of Idiopathic Interstitial Pneumonia and Their Correlation With Spirometry Findings: A Study at Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia

<b>Background:</b> Idiopathic interstitial pneumonias (IIPs) are widespread interstitial lung diseases with no known cause. The diseases are characterized by a steady decline in lung function. <b>Objective:</b> To assess the patterns of IIPs and investigate the correlation between the extents of lung involvement on high-resolution computed tomography (HRCT) with spirometric findings in Tikur Anbessa Specialized Hospital (TASH) chest clinic, covering the period from February 2020 to February 2023. <b>Methods:</b> An institution-based retrospective, descriptive, and cross-sectional study design was used. This study included all cases diagnosed with IIPs that underwent HRCT and spirometry within a 3-month window. Finally, we used the Pearson correlation test with a 2-tailed significance of less than 0.05 as a cutoff. Then the information is presented using simple frequencies, summary measures, tables, and figures. <b>Result:</b> There were 54 patients diagnosed with IIP. The overall median age of the patients was 53.9 ± 15.4. Nonspecific interstitial pneumonia (NSIP) was the most common interstitial lung disease diagnosed. Ground-glass opacity (GGO) was the most dominant HRCT feature identified. Pearson correlation tests (<i>p</i> < 0.05) were used to examine the correlation between lung involvement and spirometry parameters, as well as pulse oximetry-measured oxygen saturation. All spirometry parameters, forced vital capacity (FVC), forced expiratory volume at 1 min (FEV1), peak expiratory flow (PEF), forced expiratory flow (FEF) 25%-75%, and oxygen saturation, demonstrated a significant negative correlation with lung involvement. The strongest correlations were observed with FVC (<i>r</i> = -0.827) and FEV1 (<i>r</i> = -0.789), both with <i>p</i> < 0.001. Oxygen saturation showed a moderate correlation (<i>r</i> = -0.49, <i>p</i> < 0.001), while PEF and FEF 25%-75% exhibited weak correlations (<i>r</i> = -0.39, <i>p</i>=0.003, and <i>r</i> = -0.38, <i>p</i>=0.005, respectively). <b>Conclusion and Recommendations:</b> There was a significant negative correlation between FVC and FEV1 and the extent of lung involvement identified by HRCT in IIPs suggesting a pivotal role of pulmonary function tests (PFTs), specifically FVC, in monitoring IIP progression, supported by HRCT for diagnostic clarity. To enhance IIP patient care, routine PFTs, particularly FVC, are recommended for monitoring.